1. Field of the Invention
The present invention relates to a method of lowering a floating body of a floating foundation and carrying a structure projecting above the water surface to an end position located beneath a water level and of securing the floating body in the end position with cables or rods connected with anchors set in the ground.
2. Description of the Prior Art
Floating foundation, e.g., which are used in oil rigs, are known. Such floating foundations include a floating body that supports the weight of a structure projecting above the water surface. The structure has a portion located beneath the water surface and a portion located above the water surface and which, in case of an oil rig, includes a derrick. The sum of the buoyancy of the floating body of the floating foundation and of the buoyancy of the underwater portion of the structure correspond exactly to the weight of the entire construction, i.e., the entire construction floats in water, with the floating body of the floating foundation being located beneath the water surface. In order for the construction to retain its position above the seabed, the floating foundation is retained against a horizontal displacement relative to the seabed by cables, rods, or hawsers connected with the set in the seabed, anchors. The cables, ropes or hawsers extend at an angle to a horizontal of, e.g., 45xc2x0.
The cable, rope, hawser retaining anchors are formed dependent on the ground, e.g., as rock anchors for rock beds, as stay-bars for gravel beds . . . Conventionally, the cable-forming strings remain open (hanging loose). The end of a cable is inserted in a bore formed in the ground, and a mortar is pressed through an injection tube that extend up to the front end of the cable, providing for anchoring the cable. Other anchoring methods, e.g., using a pure mechanical clamps and the like, are also known.
A floating foundation with a floating body located beneath a water surface and retained by cables or hawsers connected with the set in the ground, anchors is disclosed in U.S. Pat. No. 5,964,550. Japanese Publication JP 06255573 discloses a construction the base of which lies beneath the water surface, with the structure projecting above the water surface, and which is held by cables or hawsers in its position, with the cables or hawsers being connected with set in the ground, anchors.
European Application EP 02 015395.3 discloses a floating foundation for a projecting above the water surface, structure which is retained in its end position beneath the water surface against a buoyancy force of at least one buoyancy body by locking devices anchored in the ground. The buoyancy force is greater than it would be necessary for retaining the floating condition of the entire construction in the end position of the floating body, i.e., the floating body, because of the amount of its buoyancy, is preloaded with respect to the locking devices. This increases the stability of the floating foundation. The displacement of the floating foundation, together with the supported structure to a predetermined site, is effected by floating it over the water surface. However, the lowering of the floating foundation to its end position is associated with a considerable underwater work, which is associated with increased costs.
An object of the present invention is to provide a method of lowering a floating foundation, which floats above the water surface, to its end position, beneath the water surface against the buoyancy of the floating body, with the underwater work being substantially reduced.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a method of lowering a floating body of a floating foundation and carrying a structure projecting above a water surface to an end position located beneath the water level, and of securing the floating body in the end position. The method includes forming, in the floating body which floats above the water surface, at least three through-openings in corner points of an imaginary triangle, securing, to the floating body above each of the through-openings, an upwardly projecting tube, and threading, through each of the upwardly projecting tubes, a cable or a rod and connecting the cable or the rod with a set-in-ground anchor.
There is provided, in a region of an upper end of each of the upwardly projecting tube, an uptake device connectable with the respective cable or rod. Then, the floating body, is lowered with the uptake devices, to its end position beneath the water surface against buoyancy of-the floating body, and the cables or rods, in its end position of the floating body, are fixedly secured thereto. Thereafter, sections of the cables or rods above fixation points of the cables or rods with the floating body are cut off, and the upwardly projecting tubes, which are located above the respective through-openings, are removed.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however both as its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.